Improvements to electronic displays now allow them to be used in outdoor environments for informational, advertising, or entertainment purposes. While displays of the past were primarily designed for operation near room temperature, it is now desirable to have displays which are capable of withstanding large surrounding environmental temperature variations. For example, some displays are capable of operating at temperatures as low as −22 F and as high as 113 F or higher. When surrounding temperatures rise, the cooling of the internal display components can become even more difficult.
Additionally, modern displays have become extremely bright, with some backlights producing 1,000-2,000 nits or more. Sometimes, these illumination levels are necessary because the display is being used outdoors, or in other relatively bright areas where the display illumination must compete with other ambient light. In order to produce this level of brightness, illumination devices (ex. LED, organic LED, light emitting polymer (LEP), organic electro luminescence (OEL), and plasma assemblies) may produce a relatively large amount of heat.
Still further, in some situations radiative heat transfer from the sun through a front display surface can also become a source of heat. In some locations 800-1400 Watts/m2 or more through such a front display surface is common. Furthermore, the market is demanding larger screen sizes for displays. With increased electronic display screen size and corresponding front display surfaces, more heat will be generated and more heat will be transmitted into the displays.
Given the well-known thermodynamic property that cool air falls and hot air rises, it was previously thought that the best way to cool an electronic display was to ingest the cool air which is found near the bottom of the display. Ingesting the warm air near the top of the display as the cooling air did not seem to make thermodynamic sense. While the air near the bottom of the display is sometimes cooler than the air near the top of the display, it was found that this is not always the case. Especially in applications where the display is mounted on a sidewalk or paved environment, heat was found to emanate from the pavement and cause the air near the bottom of the display to have a higher temperature than the air found at the top. Further, the environment near the bottom of the display was found to contain various contaminants such as dirt, dust, water, leaves, and even garbage/waste materials. These contaminants can have an adverse effect on the display if ingested or clogging up the cooling air intake.
Also, when cooling air was used to cool the rear portion of an electronic display (sometimes an LED backlight or LED display) it was found that the area where the cooling air was ingested was maintained at a cooler temperature than the area where the cooling air was exhausted. Temperature variations across an electronic display may be undesirable as they can alter the optical performance of the electronic display. Some components perform differently when subjected to different ambient temperatures. Thus, with temperature variations across an electronic display there can be visible variations in the image generated by the electronic display.